👷 Travis: Use test matrix

.travis.yml

@@ -1,15 +1,13 @@
-language: python
+matrix:
-python:
+  include:
-  - "2.6"
+    - python: 2.7
-    dist: trusty
+    - python: 3.4
-  - "2.7"
+    - python: 3.5
-  - "3.2"
+    - python: 3.6
-    dist: trusty
+    - python: 3.7
-  - "3.3"
+      dist: xenial
-    dist: trusty
+      sudo: true
-  - "3.4"
+
-  - "nightly"
-sudo: false
 
 # command to run tests
 script: py.test